GDM login screen: sometimes both user list and avatar+input are shown
Please take a look at my photo (second username censored but I hope you will see what's the problem):
This is GNOME 3.36 on Fedora 32 but I had the same problem with 3.34 on F31 and 3.32 on Arch Linux. It seems to be longstanding.
This bug is only visible if one long running GNOME session is used for GDM login screen and only after at least a few hours after starting it. By default GDM uses Wayland and kills its greeter session a few seconds after successful login. When Wayland is disabled in GDM, Xorg is used instead and GDM is not able to kill greeter GUI session — in this case one long running session is used.
This means that to reproduce this issue you have to disable Wayland in GDM (/etc/gdm/custom.conf, uncomment proper line), reboot and keep computer running for a few hours. It may be good idea to have two user accounts and switch between them regularly.
It seems to me this bug is in the shell or mutter since it's graphical bug. Please move this issue if I am wrong.